Carrier wave transmitter



June 27, 1939. wfr. D11-@HAM 2,163,670

v CARRIER WAVE TRANSMITTER Filed Feb. 5, 1936 I 1NV ENT OR.

l wmfoncHAM w ATTORNEY.

Patented June 27, 1939 UNITED STATES PATENT OFFICE A 2,163,670 CARRIER WAVE TRANSMITTER Application February 3, 1936, Serial No. 62,020 In Great Britain February 25, 1935 Claims.

. ating those oscillations or in a circuit of an amplier driven by the oscillator and then to sub-ject the modulated oscillations to further amplification in a power amplifier before actual transmission, e. g., before radiation from an antenna. The advantage of effecting modulation in this manner at a comparatively early stage of the transmitter, i. e., at a stage where the power level is low is that it is a relatively simple matter to effect deep modulation without material distortion; in other words, it is a relatively simple matter to obtain substantially rectilinear modulation if modulation be applied at an early stage where the power is low. In practice, however, with this type of transmitter difficulty is experienced in avoiding distortion in and by the power amplifier which is between the stage at which modulation is effected and the antenna or other output circuit of the transmitter. In high power transmitters, this difficulty becomes very serious for if with known arrangements the operating conditions be made such that there is'no risk of distortion, the said conditions will not be such as will give good efficiency.

The principal object of the present invention is to avoid this difficulty and to provide an improved transmitter of the kind wherein amplification of the modulated carrier wave energy is effected.

According to this invention in a transmitter of the kind wherein the carrier wave oscillations are modulated so that substantially distortionless modulated carrier wave energy appears in a circuit which is followed by an amplifier 4for amplifying said modulated carrier wave energy, means are provided for differentially combining energy derived from said circuit and from a circuit of the amplifier which follows it and utilizing the differentially combined energy to apply compensation at a point in the transmitter preceding said amplifier in such manner that so long as a predetermined relationship exists between the two differentially combined energies, no compensation is applied, but if said predetermined relationship isv departed from, compensation is applied in such direction as substantially to compensate for that departure.

There will now be described with reference to Figs. 1, 2 and 3, of the accompanying diagrammatic drawing, three embodiments of the invention as applied to transmitters of the series modulation type. It is, however, to be understood that the invention is not limited to such trans- :.5 mitters, but is of general application irrespective of the type or method of modulation employed.

Referring to Fig. l, high frequency carrier wave oscillations from a source are applied via a coupling at O between the control grid and 10 the cathode of a high frequency amplifier tube VI, whose anode-to-cathode space is in series with the anode-to-cathode space of a modulating tube V2, the arrangement preferably being the usual series modulation arrangement sho-wn 15 and wherein a series circuit extends from the positive terminal of a source of anode potential I0 from the anode to the cathode of the high frequency amplifier tube VI, then through a choke CH to the anode of the modulating tube 20 V2, from the anode to the cathode of the said modulating tube, and then to earth and the negative terminal of the source of anode potentialy l0. Modulating potentials are applied from 'a source I2 via transformer lVf through a suit- 25 able coupling condenser CC between the control grid and the cathode of the modulating tube V2. The grid-to-cathode circuit of this modulating tube includes in series the usual grid resistance, a source B of suitable negative bias pc- 30 tential, and two bias resistances RI, R2. Connected to the anode of the high frequency tube VI is the usual tuned output circuit LCI which in turn is coupledby a condenser IlIto the grid of a power tube V3 which serves to amplify the 35 tuned output circuit LCI of thehigh frequency 4,0A

tube'VI at which modulation is effected is a coil MA which is in series in a loop circuit with a suitable rectifier DI, e. g., a diode, and a smoothing inductance SL and condenser SC and the terminals of this condenser are connected across 45 the resistance RI. Coupled to the inductance in the tuned output circuit LCZ of the power tube V3 is an inductance PA which is similarly in series with a loop circuit with a rectifier D2, smoothing inductance SLI, and condenser SCI 50 and the said condenser SCI is connected across the other bias resistance R2 in the grid-cathode circuit of the modulating tube V2. The sense of connection of the rectiflers is such that rectified potentials set up across the bias resistance RI 55 oppose those across the bias resistance R2 and the adjustments of the circuits are such that as long as the modulated carrier wave energy in the output circuit LC2 of the power tube V3 is an accurate repetition of that in the output circuit LCI of the high frequency tube Vl, the algebraic sum of the potentials set up across the two bias resistances Rl R2 is zero. If, however, the modulated carrier wave energy in the output circuit LC2 ceases to be an accurate repetition of that across one of the two series-connected bias resistances RI, R2 will becomegreater than that set up across the other with the result that the total grid bias upon the modulating tube V2 will vary in a direction and to an extent suflicient to cause compensation for the distortion in question.

In some cases it will not be found sufficient to add the rectified potentials from the rectiers directly in the direct current grid circuit of the modulating valve and in such cases a direct current amplifier maybe interposed; in other words, the two bias resistances Rl, R2 which in Fig. 1 are in the grid-cathode circuit of the vmodulating tube V2, may be as shown in Fig. 2 included instead in the grid circuit of aV direct current amplifier tube V0, and the anode ofthistube may be connected through a suitable source of fixed bias Bl in series with a grid resistance to the grid of the modulating tube `V2,'the anode of the said direct current amplifier tube Vl! being also connected to a suitable source of anode potential, such as source I0, through a resistanceAR and also through 'a further resistance R3 to the common cathode point of theV modulating tube' V2 and the said direct current amplier tube Vl).

The systems'illustrated in Figs. 1 and 2 can be arranged to provide automatic compensation for distortion arising by reason of departure from rectilin-earity both at the upper and lower bends of the characteristic curveY of the power amplifier tube. Where, however, it issuii'icient to provide for compensation for curvature at or near one end only of the characteristic ofthe power amplier tube, a somewhat simpler arrangement can be used, this simpler arrangement employing only a single rectifier.' In-this simplied arrangement, which is illustrated in Fig. 3, the output circuit of the power amplifier tube V3 (no-t shown in Fig. 3) and the output circuit of the tube Vl atwhich modulation is eiected (also not shown in'Fig.- 3) are'diierentially coupled via coils'MAl, PAI, respectively, to a common coil RC which is in series in a-loop circuit with a rectifier D3, a smoothing inductance SLZ, and a condenser SC2, and this condenser has its terminals connected across a single bias resistanceRll, which is in series with afixed bias source' B2 and a grid leak between'grid and cathode of the modulating tube V2.

It will be appreciatedthat it' is 'not necessary in carrying out'this invention to utilize' the differentially combined potentials to vary the grid bias of the modulating tube; for example; the said differentially combined potentials Ymay be utilized to'- provide the required compensation by varying the grid biason the power amplifier tube itself. In general, however, the specifically described method ofY varying the grid bias upon the modulating tube is preferred since if control be effected by varying the lgrid bias upon a power amplifier,- tube, disturbing effects due to grid, current are likely to'occur.

What is claimed is:

1. In a signalling system, a plurality of electron discharge tubes each of which has input and output electrodes, alternating current circuits for impressing wave energy of carrier wave frequency on the input electrodes of one of said tubes and from the output lelectrodes of said one of said tubes to the input electrodes of another of said tubes, a modulating impedance variable at, signal frequency connected with an electrode in the output circuit LCI, the potential set up'Y in said one of said tubes to modulate said wave Venergyyand supplemental means for additionally modulating said wave energy when the modulated wave energy in the output of said other of said tubes is not a substantial repetition in wave form of the modulated wave energy in the output of saidone of said tubes, including rectifying means differentially coupling an electrode of each of said tubes to said modulating impedance to additionally control the impedance thereof.

2. In a signalling system, a pluralityof electron discharge tubes each of which has input and output electrodes, alternating current circuits for impressing wave energy of carrier Wave frequency on the input electrodes of one of said tubes and from the output electrodes of Asaid'one of said tubes to theV input electrodes of another of said tubes, a modulating impedance controllable at signal frequency connected with an electrode in said one cfsaid tubes to modulate therein said wave energy, a supplemental impedance connected with said modulating impedance for regulating the value of said controllable modulating impedance,l and differential circuitsl including `rectifying means coupling the output electrodes of each of said-tubes to said supplemental impedance to impress additional controlling potentials thereon when the modulated wave energy in said other of said tubes is not substantially a repetition in wave form of the modulated wave energy in said one of said tubes.

3. In a signalling system, a plurality of electron discharge tubes each of which has input and output electrodes, high frequency alternating current circuits for impressing wave energy on the-input electrodes of .one of said tubes and from the output lelectrodes of saidone of said tubes to ther input electrodes of another of said tubes, a modulating impedance variable at signal frequency connected with an electrode in said one of said tubes to-modulate said Wave energy, a pair of supplemental impedances connected with said modulating impedance for regulating the value of said modulating impedance, and rectifiers differentially'coupling the output electrodes of each of said tubes to said supplemental impedances.

4. In a signalling system, a plurality of discharge devices each having a control electrode, an anode and a cathode, alternating current circuits for impressing wave energy on the control electrode and cathode of one of said devices and from the anode and cathode of said one of said devices on the control electrode and cathode of another of said devices, a modulating tubehaving electrodes, the impedance between a'pair of which is connected in series with the impedance between the anode and cathode of said one of said electron discharge devices, means for impressing modulating potentials on an' electrode of said modulating tube, supplemental means for impressing' other potentials on an electrode of said modulating tube when the energy Yin said other of said devices is not a substantial repetition oftheV energy in saidlonedevice, andcircuits each including a rectifier coupling said supplemental means differentially to the output electrodes of said one of said devices and to the output electrodes of said other of said devices.

5. In a signalling system, a plurality of electron discharge devices each having a control electrode, an anode and a cathode, alternating current circuits for impressing wave energy on the control electrode and cathode of one of said devices and from the anode and cathode of said one of said devices on the control electrode and cathode of another of said devices, a modulating tube having a control grid, an anode and a cathode, means connecting the impedance between the anode and cathode of said tube in series with the impedance between the anode and cathode of said one of said discharge devices, means for impressing modulating potentials on an electrode of said modulating tube, supplemental means for impressing correcting potentials on an electrode of said modulating tube when the energy in the output of said other of said devices is not a substantial repetition of the energy in the output of said one of said devices, and circuits including rectii'lers coupling said supplemental means differentially to the output electrodes of said one of said devices and to the output electrodes of said other of said devices.

6. In a signalling system, a plurality of electron discharge devices each having a control electrode, an anode and a cathode, alternating current circuits for impressing wave energy on the control electrode and cathode of one of said devices and from the anode and cathode of said one of said devices on the control electrode and cathode of another of said devices, a modulating tube having electrodes including a control grid and a cathode, a circuit connecting the impedance between a pair of the electrodes in said tube in series with the impedance between the anode and cathode of said one of said discharge devices, means for impressing modulating potentials on the control grid of said modulating tube, supplemental means for impressing other potentials on the control grid of said modulating tube when wave distortion occurs in said devices or circuits, and circuits including rectiers coupling said supplemental means diierentially to the output electrodes of said one of said devices and to the output electrodes of said other of said devices.

'7. In a signalling system, a plurality of electron discharge devices each having a control grid, a cathode and an anode, alternating current circuits for impressing wave energy on the control grid and cathode of one of said devices and from the anode and cathode of said one device to the control grid and cathode of another of said devices, a modulating tube having an anode, a cathode and a control grid, circuits connecting the anode and cathode of said modulating tube in series with the anode and cathode of said one of said electron discharge devices and with a source of direct current potentials, means for impressing modulating potentials on the control grid and cathode of said modulating tube, a circuit for impressing a biasing potential between the control grid and cathode of said modulating tube, a pair of impedances in said circuit, a pair of rectifiers having input electrodes and having output electrodes differentially connected with said pair of impedances and a coupling between the input electrodes of one of said rectii'lers and the anode and cathode of said one of said electron discharge devices and between the input electrodes oi the other of said rectiers and the anode and cathode of the other of said electron discharge devices.

8. In a signalling system, a plurality of electron discharge devices each having a control grid, a cathode and an anode, alternating current circuits for impressing wave energy on the control grid and cathode of one of said devices and from the anode and cathode of said one device .to the control grid and cathode of another of said devices, a modulating tube having an anode, a cathode and a control grid, circuits connecting the anode and cathode of said modulating tube in series with the anode and cathode oi said one of said electron discharge devices and with a source of direct current potentials, means for impressing modulating potentials on the control grid and cathode of said modulating tube, a circuit for impressing a biasing potential between the control grid and cathode of said modulating tube, an impedance in said circuit, an amplifier tube having input electrodes and having output electrodes connected to said impedance, a pair of rectiers having input electrodes and having output electrodes dierentially connected with the input electrodes of said ampliiier tube, and a coupling between the input electrodes of one of said rectiflers and the anode and cathode of said one of said electron discharge devices and between the input electrodes of the other of said rectiers and the anode and cathode of the other of said electron discharge devices.

9. In a signalling system, a plurality of electron discharge devices each having a control grid, a cathode and an anode, alternating current circuits for impressing wave energy on the control grid and cathode of one of said devices and from the anode and cathode of said one device to the control grid and cathode of another of said devices, a modulating tube having an anode, a cathode and a control grid, circuits connecting the anode and cathode of said modulating tube in series with the anode and cathode of said one of said electron discharge devices and with a source of direct current potentials, means for impressing modulating potentials on the control grid and cathode of said modulating tube, a circuit for impressing a biasing potential between the control grid and cathode of said modulating tube, a rectier having input electrodes and having output electrodes connected with said last named circuit, a coupling between the input electrodes of said rectifier and the anode Vand cathode of said one of said electron discharge devices and a coupling between the input electrodes of said rectifier and the anode and cathode of the other of said electron discharge devices said couplings being differential.

10. In a signalling system, a plurality of electron discharge amplifying devices each having a control electrode, an anode, and a cathode, a source of oscillations of carrier wave frequency, an alternating current input circuit coupling the control electrode and cathode of one of said devices to said source of oscillations, an alternating current output circuit coupling the anode and cathode of said one of said devices to the control electrode and cathode of another of said devices, an alternating current output circuit connected with the anode and cathode of said other of said devices, a source of modulating potentials, an additional electron discharge device having an anode, a cathode, and a control grid, a circuit coupling the control grid and cathode of said additional device to said source of modulating potentials, a circuit including a ferentially to said impedanca'a 'circuit Ycoupling the Vinput electrodes of one of said rectiers to the output circuit connected with the output elec trodes of said onel of said devices, and a circuit coupling the input electrodes of the other of said rectiers to the output circuit coupled with the output electrodes of said other of said devices. WILLIAM THEODORE DITCHAM. 

